An elevator typically comprises an elevator car and a counterweight, which are vertically movable in a hoistway. These movable elevator units are interconnected to each other by a suspension roping that suspends them on opposite sides of rope wheels mounted above the movable elevator units. For providing force for moving the suspension roping, and thereby also for the elevator units, one of the wheels is typically a drive wheel engaging the suspension roping, which drive wheel is rotated by motor. The motor is typically automatically controlled by an elevator control system.
In elevators, the roping comprises at least one but typically several ropes passing alongside each other. There are elevators where the ropes are belt-shaped, i.e. they have a cross section with width substantially greater than the thickness thereof. Position of the belt-shaped ropes relative to each rope wheel around which they pass (in the axial direction of the wheel) as well as relative to other ropes needs to be controlled so that adjacent ropes do not drift too close to each other, and so that none of the ropes drifts in said axial direction away from the circumferential rope contact area of the wheel against which the rope in question is intended to rest. One way to control this axial position of the belt-shaped ropes is to shape the circumferential rope contact areas of the wheel cambered. Each cambered circumferential rope contact area has a convex shape against the peak of which the rope rests. The cambered shape tends to keep the rope passing around it positioned resting against the peak thereof, thereby resisting displacement of the rope away from the point of the peak.
In prior art, a drawback has been that there has not been a simple and efficient way to monitor the position of ropes. Particularly, this has been difficult in case where the rope wheel is a cambered rope wheel.